The present invention relates to a multi-head sewing machine provided with a plurality of sewing heads and a method of controlling operation of the multi-head sewing machine. In particular, the present invention relates to a vibration reduction mechanism in a multi-head sewing machine for reducing vibration that may be generated with driving of a needle bar to a sewing machine body and a method of controlling operation of the multi-head sewing machine.
Heretofore, in a sewing machine provided with a needle bar that moves up and down in response to rotation of an upper shaft, a vibration reduction mechanism is known in which in order to reduce vibration generated in an up-and-down direction (vertical direction) of the needle bar with the up-and-down motion of the needle bar, a rotation type of eccentric weight that moves at substantially an opposite phase to that of the up-and-down motion of the needle bar is provided, and inertia force in the up-and-down direction of the needle bar is negated by causing this rotation type of eccentric weight to operate. In the vibration reduction mechanism conventionally known in the art, in order to simplify its configuration, the rotation type of eccentric weight rotates with an upper shaft by disposing the rotation type of eccentric weight on the axis of the upper shaft. However, in such a configuration, vibration generated in the up-and-down direction of the needle bar can be reduced, but vibration generated in a right-and-left direction (horizontal direction) perpendicular to the up-and-down direction (vertical direction) of the needle bar cannot be reduced.
Thus, as one example for solving the defect described above, for example, a vibration reduction apparatus for a sewing machine disclosed in Patent Document 1 below is proposed. In the vibration reduction apparatus disclosed in this Patent Document 1, another weight (balancer) other than the rotation type of eccentric weight is disposed on a predetermined axis provided separately from the upper shaft, a conversion mechanism for converting rotation of the upper shaft into an opposite direction thereof to transmit it to the balancer is provided, and the balancer disposed on the predetermined axis is caused to rotate in an opposite direction to a rotational direction of the upper shaft via the conversion mechanism. In such a configuration, since the rotational direction of the upper shaft for driving the needle bar (rotational direction of the rotation type of eccentric weight) and a rotational direction of the balancer become opposite, not only vibration generated in the up-and-down direction of the needle bar can be reduce, but also vibration generated in the right-and-left direction (horizontal direction) of the needle bar can be reduce.                [Patent Document 1] Japanese Patent Application Laid-open Publication No. 7-328269        
Now, by applying a technique disclosed in the above Patent Document 1 to a multi-head sewing machine provided with a plurality of sewing heads, vibration to a sewing machine body generated with up-and-down motion of a needle bar can also be reduced. As described above, in the above-mentioned vibration reduction mechanism for causing the balancer to rotate in the opposite direction to rotation of the upper shaft, which causes the needle bar to move up and down, the conversion mechanism for converting the rotation of the upper shaft into the opposite direction thereof and transmitting it to the balancer is required. However, as is known in the prior art, in one of the plurality of sewing heads installed in the multi-head sewing machine, various mechanical elements (for example, a needle bar, a thread take-up lever, a press foot, a needle bar case and the like) have already been configured and disposed complicatedly for a sewing operation of the sewing machine. In the case where the vibration reduction mechanism including the conversion mechanism described above is further added to such a sewing head, not only the configuration of the sewing head becomes more complicated, but also harmful effects occur that the sewing head has to be made larger. In addition, costs of the multi-head sewing machine become increased, and thus, it is very inconvenient.